The role of complement in immune reactions is to be examined using mouse strains which are "normal," deficient in C5. or which have an unusually high level of hemolytic complement. Furthermore, the sensitivity of different cells to complement mediated cytolysis is to be examined with special attention to an easily eluted macromolecule which appears to mediate auto-anticomplementarity. BIBLIOGRAPHIC REFERENCES: Amkraut, Alfred A., Rosenberg, Leon T., and Corp, Richard B. Univalent activation of anaphylactic reactions. Immunochemistry, 12:523-25, 1975. Mongini, Patricia K.A., and Rosenberg, Leon T. Inhibition of lymphocyte trapping by cell-free ascitic fluids cultivated in syngeneic mice. J. Immunol., 114(2), 650-54,1975.